1. Field of the Invention
The present invention relates generally to electrical equipment and process using backup batteries, and more particulary, to processes and circuits indicating the operation of a backup battery used in a electrical equipment, such as a communication equipment, and a circuit for sensing the operation.
2. Description of the Prior Art
Typically, a backup battery is used in an electrical equipment to automatically supply power to the equipment when external power supply is cut off or the equipment is plugged out. This is especially true for an communication equipment. Unless a communication equipment always has a power source, communications that had been transmitted may be forever lost. Further, during emergencies, this may be dangerous to human lives that depend on information that are transmitted and received from the communication equipment. When a backup battery is being used for a communication equipment, a user cannot know that the communication equipment is being operated by the backup battery. As a result, the user cannot recognize the external power interruption, which may simply be treated, until the communication equipment is stopped in operation as electricity charged in the backup battery is completely exhausted. Thus an indicator of a use of the backup battery is useful.
On this matter, an exemplar of the contemporary practice, Dougherty, U.S. Pat. No. 5,549,984, Control And Indicator Circuit For A Dual Battery System, issued on the 27.sup.th day of August 1996, discusses a battery backup or dual battery system and particularly discusses a control circuit for switching between the battery switch in a dual battery system. Another exemplar. Chen, U.S. Pat. No. 5,528,149, Test Circuit For Back-Up Battery, issued on the 18.sup.th day of June 1996. discusses a test circuit for a back-up battery which includes a main switch which connects a main power source to a load, and a diode which is interposed between a back-up battery and the load. Huhndorff el al., U.S. Pat. No. 5,525,439, Battery Voltage Tester For End Of Cell Having Indicator Disposed On Battery Side, issued on the 11.sup.th day of June 1996, discusses a battery with an end-of-cell voltage indicating device which can be used to indicate the state-of-charge of the battery. The indicating device has a flexible substrate of the same peripheral configuration as the battery. Yoshimatsu, U.S. Pat. No. 5,473,262, Power Source Residual Capacity Measuring Apparatus And Power Source Apparatus Having Power Source Capacity Measuring Circuit, issued on the 5.sup.th day of December 1995, discusses a power source residual capacity measuring apparatus which comprises a circuit for measuring a residual capacity of a power source, a circuit for detecting a current flowing in a load connected to the power source, and a circuit for correcting the residual capacity of the power source which was measured by the measuring circuit. Landau et al., U.S. Pat. No. 5,454,710, for a Display System For A Battery Monitoring Circuit, issued on the 3.sup.rd day of October 1995, discusses rechargeable batteries, especially a circuitry for controlling the charging operation and monitoring the parameters of the battery during and after the recharging of operation. Aita et al., U.S. Pat. No. 5,122,751, for a Device For Detecting Residual Capacity Of A Battery Both In Load And No Load Conditions, issued on the 16.sup.th day of June 1992, discusses a device for detecting and displaying residual capacity of a battery which comprises a comparator comparing detection voltages set to predetermined values and open circuit voltage. From the study of these exemplars of the contemporary practice and of the prior art, I find that there is a need for an effective and improved sensing circuit and a method of using such a sensing circuit to indicate use of a backup battery, as in the particulars of the present invention.